1. Field of the Invention
This invention relates to an improved pipelock comprising a first pair of rings facing each other axially, with the inner diameter of each ring at the outer face being smaller than the inner diameter of each ring at the inner face, each of said first pair of rings comprising at least two circumferential parts, means to restrain longitudinal movement of facing circumferential parts outwardly from each other, at least one second ring comprised of at least two circumferential parts connected to each other, outwardly surrounding said first pair of rings, and constraining outward radial movement of said first pair of rings, at least one third ring comprised of at least two circumferential parts having an outer surface conforming to the inner surface of said first pair of rings, and at least one waffled fourth ring comprised of at least two circumferential parts having an outer surface in contact with the inner surface of said third ring.
2. Information Disclosure Statement
Circumferential and axial cracks tend to develop in piping systems subjected to stress corrosion cracking. These cracks generally occur in the heat-affected zones wherein pipes have been welded together and extend not only circumferentially around the pipe, axially along the pipe, but also through the thickness of the pipe wall. The pipes thus lose their strength and will separate from each other, resulting in leakage of the medium contained therein.
Pipes with detected cracks have been repaired by a weld overlay. However, once cracks have begun in the pipes they can also penetrate through the additional weld overlay. For such reason weld overlays have not been successful in eliminating the danger of circumferential cracks that develop in piping systems.
In application Ser. No. 539,074 for Novel Pipelock, filed Oct. 4, 1983, Jan S. Porowski and William J. O'Donnell, disclosed and claimed a pipelock for holding the ends of pipe or pipe fittings together, even if the cracks referred to above extend around the entire circumference of the pipes or pipe fittings and/or through the walls thereof. The Porowski et al pipelock also produces axial and circumferential compressive stresses at the weld location, thus reducing crack growth rates.
However, since the outer surface of a pipe is almost never axisymmetric, the application of the Porowski et al pipelock thereto will not result in the conformance of the inner surface of said third ring with the outer surface of the pipe. To fabricate a third ring whose inner surface conforms to the outer surface of the pipe, or to machine the outer surface of the pipe to conform to the inner surface of the third ring, would be prohibitively expensive. In reference to the latter possible modification, removal of material from the pipe surface is further highly undesirable, since the thickness of the pipe wall would be reduced. And yet effective contact between the inner surface of the third ring and the outer surface of the pipe is needed in order to effectively hold pipes on both ends of the pipe weld securely in place.